Green screen to alpha?

I let a friend make a private area on my land.
I told him he could use 80 prims.
He made a lovely place using 400 prims.

I'm now trying to show him how to make the place look the same using texturing.

He does not have Photoshop and I don't have the time to do it myself so what I am looking for is an easy way for him to drop the high prim items in my green room and take a snapshot and then have the green converted into pure transparent.

I know about the halo issue of the other programs, but in this case the program could eat a row of pixels before it is reduced in resolution for upload.

I have also found that I can get perfect color by disabling fog. This means that the alpha conversion is a simple matter of replacing all pixels that are the exact color.

I know that this is not optimal, but I am looking for a simple tool that will convert the texture into the TGA file.

The Gimp is totally free.

Graphic Converter is free on the Mac, as is The Gimp.

the gimp, select by color, and the color to alpha filter (i use the print screen key to snag images, therefore theres no resizing and no fuzzy green edges to deal with, resize before upload)

Attach parts of the building onto your HUD to take the snapshot. You don't need to mess with the fog or contend with perspective distortion.